Trim the base of the lettuce, then wash and dry the leaves and cut them thinly.
Cut the cherry tomatoes in half (the larger ones into wedges).
Finely slice the spring onions. Cut the avocados in half (lengthwise), remove the stone, peel and dice the flesh. Squeeze some lemon juice over it.
Dice the feta and sprinkle some dried oregano over the cubes.
Finely chop the mint and the parsley.
Whisk the lemon juice with the olive oil, season with salt and pepper.
Put the chicken, lettuce, tomatoes and spring onion in a large serving bowl, then toss with the dressing. Gently fold in the avocado pieces, olives and feta cubes.
Taste and adjust the seasoning, lemon juice and oil to your liking.